Shrinkage cracks in soil function as a dominant control on the partitioning and distribution of moisture fluxes in the vadose zone. Their dynamics influence the moisture balance and control water availability for runoff, deep infiltration, and near-surface storage. We present a new low-cost field instrument to monitor the temporal change in crack volume as affected by shrinkage and swelling cycles. The proposed crack-o-meter is composed of a sealed impermeable bag connected by a hose to a standpipe. An automated level logger records changes in the water level in the standpipe, which correspond to volumetric changes of the crack. The results from two laboratory experiments showed that the volume change observed by the crack-o-meter instrument scales linearly with the actual volume change, with an average error of 3%. The instrument was then used in a field experiment in Chile, where it measured the closing of cracks due to soil swelling.